1. Field of the Invention
The present invention relates to an improvement made to devices for the heat treatment of moving yarns, especially the heat treatment of yarns so as to impart to them certain shrinkage and/or bulkiness and/or elasticity properties.
2. Discussion of the Related Art
In all yarn conversion processes requiring a heat treatment, the main problem which arises is that of rapid heat transfer, the heat having to rise uniformly in the core and in the same way over the entire length of the yarn. In fact, as is known, the temperature of the treatment and its uniformity have a very great influence on the quality of the yarn.
It is well known that heat treatment varies depending on the substance treated, on the yarn count and on the speed at which it passes through the oven. Thus, it is easily understood that the core is more rapidly reached with a fine yarn than one having a high count. Likewise, it is known that it is not possible to heat a yarn above a certain ceiling temperature, without it suffering degradation. Consequently, since this question of heat exchange is very important in the field of texturizing, very many solutions have been envisaged in order to solve it, these solutions involving the three great principles of heat exchange, namely convection, radiation, and conduction (direct contact with the heating surface).
Over and above this problem of good heat transfer there also arises that of keeping the yarn under a defined tension, depending on the treatment which takes place. Thus, for example, in the case of a stretching operation, possibly combined with a texturizing operation, it is necessary that the yarn be kept under a maximum tension, while on the other hand, when it is desired to shrink the yarn, the tension has to be reduced. Finally, the problem also arises of increasing the production speeds on a textile machine, this having passed from a few tens of meters per minute thirty or so years ago to a thousand meters, or even more, today, and this has had the consequence of leading to very sizable installations, ovens becoming longer and longer, possibly reaching as much as two meters long.
Among the various solutions proposed for obtaining very good uniformity of heat transfer and also for easing the problems of temperature regulation from position to position on a machine so that the entire production is homogeneous, it has for a very long time been envisaged to carry out heat treatments which could be termed "sequential", by producing ovens along the length of which there is a plurality of separate heat treatment zones following one after the other. Among these solutions, mention may be made of the one forming the subject of the French Patent No. 1,204,634 (corresponding to the U.S. Pat. No. 3,015,872) in which two successive treatments are carried out inside one and the same oven, one during which the yarn is subjected to a temperature considerably higher than that of the normal temperature to which it has to be heated, and this for a time such that it is not damaged, this first phase being followed by an equilibrating treatment at a temperature heating the yarn at a conventional temperature.
Such a solution, used industrially since 1953 on machines marketed by the Company HOBOURN AERO COMPONENTS Ltd., under the reference "HOBOURN--E.P.1", which is attractive because it enables the length of the ovens to be considerably decreased for a given run speed, has, however, been abandoned for a very long time by the manufacturers of textile equipment, which may be explained by the fact that it required apparatuses of complex design which were difficult to operate.